In the field of molecular nano-electronics, semiconductor nano-crystals, nanowires (NWs) and carbon nanotubes (CNTs) are becoming more and more important as components for various electronic devices. These NWs and CNTs are unique for their size, shape and physical properties and have, depending on their electrical characteristics, been used in electronic devices such as e.g. diodes and transistors. Although a lot of progress has been made on both fabrication and understanding of the limits of performance of these NWs and CNTs, there are still key issues to be addressed for potential technological applications.
In the last years, a lot of effort has been put in the synthesis of elongated nanostructures such as nanowires. Due to their restricted size, these structures exhibit novel physical and chemical properties and have opened up a large new field of basic research as well as possible applications. Metallic nanowires show high potential for being used in a wide range of advanced applications. Copper, for example, is of particular interest because of its high electrical conductivity. With rapid shrinking in size of electronic devices, copper nanowires may play an essential role to form interconnects in devices in nano-electronics and opto-electronics.
In Adv. Mater. 2001, 13(1), 62-65, Molares et al. report the fabrication of cylindrical poly- and single-crystalline copper wires by means of a template method. Copper wires with diameters between 60 nm and 500 nm and aspect ratios (ratio of length to diameter) up to 500 can be obtained. A disadvantage of the method may be that the use of a template is required for obtaining free-standing wires.
The growth of CuO nanowires by heating Cu in an oxygen atmosphere has been reported in the past (Xuchuan et al., Nano Letters, 2(12), 2002, pp. 1333-1338). However, the method described in this paper may be relatively slow, i.e. it may take several hours to grow the nanowires, and may require high temperatures, i.e. temperatures of up to 700° C.
Yong et al. reported reduction of CuO to form Cu nanowires in a plasma (Nanotechnology 18 (2007) 035608 (4 pp)). Aligned Cu nanowires were prepared by the reduction of aligned CuO nanowires in electron cyclotron resonance (ECR) hydrogen plasma at room temperature.
CuO appears to be the only material that can be used presumably because problems can occur if the heating step just results in evaporation from the surface instead of growing wires, e.g. for volatile compounds starting from about 150° C.